An Electronic Detector System for Recovering Internally 

 Tagged Menhaden, Genus Brevoorfia 



By 



R. 0. PARKER, JR., Fishery Biologist 



National Marine Fisheries Service 



Atlantic Estuarine Fisheries Center 



Beaufort, North Carolina 28516 



ABSTRACT 



Operation and results are described of an electronic detector-recovery system for 

 fish with internal ferromagnetic tags. The system does not interfere with the oper- 

 ation of fish reduction plants. Date and location of recapture can be obtained since 

 tagged fish are detected and recovered as they are landed. Growth rates of 3.1 and 

 7.2 mm per month were obtained for two menhaden out 130 and 483 days. Scale anal- 

 yses supported annulus formation assumption. The best location for tag injection in 

 adult menhaden appears to be about 13 mm above and just forward of the origin of the 

 pelvic fin. Tag incisions were healed in 85'^r of the fish recaptured after 10 days. 



INTRODUCTION 



In most fish tagging studies the recovery of 

 the tagged fish is desirable. Tags recovered by 

 magnets in scrap conveyors in all menhaden re- 

 duction plants along the Atlantic and Gulf coasts 

 of the United States are providing adequate in- 

 formation on migration patterns and mortality 

 rates (Dryfoos, Cheek, and Kroger'). Tagged 

 fish recoveries, however, in addition to providing 

 the above information, permit the determination 

 of: growth rates, validity of aging techniques, 

 best tag injection location, and time for tag in- 

 cisions to heal. 



The isolation of tagged fish from millions of 

 fish being processed has presented difficulties to 

 many investigators. Mechanical means of catch- 

 ing, handling, and processing large quantities of 



^ Dryfoos, R. L., R. P. Cheek, and R. L. Kroger. At- 

 lantic menhaden tagging studies, 1966-1969. Unpub- 

 lished manuscript. National Marine Fisheries Service, 

 Atlantic Estuarine Fisheries Center, Beaufort, N.C. 

 28516. 



menhaden and other industrial fish makes visual 

 detection and recovery of marked fish imprac- 

 tical. Photoelectric detection of marked men- 

 haden was unsuccessfully attempted by Reintjes 

 (1963). Dahlgren (1936) was the first to 

 develop a successful detector-recovery system 

 for fish with metal body cavity tags. The 

 system was improved by Hart and Tester 

 (1937). 



Our detector-recovery system was developed 

 to recover menhaden tagged with a 14-mm in- 

 ternal ferromagnetic tag or the 1-mm Bergman- 

 Jefferts' microwire tag (Jeff'erts, Bergman, and 

 Fiscus, 1963). The microwire tag could not be 

 detected at menhaden plants because of the in- 

 terference of machinery. These tags, unlike our 

 larger tags, cannot be easily distinguished from 

 the other metal recovered on magnets. Conse- 

 quently, attempts to use the microwire tag for 

 menhaden were discontinued. 



" The mention of trade names in this publication does 

 not imply endorsement by the National Marine Fisheries 

 Service. 



